Composite structure, fired body having composite structure, powder including particle having composite structure, and dielectric element including dielectric having composite structure

ABSTRACT

A composite structure including a conductor region that is configured from a first oxide, and an insulator region that is configured from a second oxide and that surrounds the conductor region, wherein the first oxide and the second oxide are in hetero structure with each other. A powder and a fired body each having such a composite structure are also preferable.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a composite structure, a fired bodyhaving a composite structure, a powder including a particle having acomposite structure, and a dielectric element including a dielectrichaving a composite structure.

Description of the Related Art

As electronic equipment is reduced in size and increased infunctionality, capacitors small in size and high in capacitance, such asmultilayer ceramic capacitors, have been progressively developed.Ceramic capacitors are excellent in output density because no chemicalreaction is interposed in the course of energy storage. On the otherhand, such ceramic capacitors are low in storable energy, and thus aceramic capacitor having a high capacitance can be developed to therebyallow for applications to not only electronic components, but alsoenergy storage devices and the like.

Examples of materials for realizing an increase in capacitance includeconductor/insulator composite materials which are important candidatesbecause of their excellent dielectric properties. Specifically, variouscomposite materials such as a metal/dielectric combination, ametal/polymer combination and a semiconductor/dielectric combinationhave been heretofore studied, and dielectric properties thereof havebeen reported. A known semiconductor/dielectric combination is a grainboundary insulation-type semiconductor capacitor.

One approach for increasing the capacitance of a capacitor by use ofsuch a composite material is to reduce the proportion of insulators toconductors. A capacitor, however, with a conductor/insulator compositematerial, which is reduced in the proportion of insulators, has theproblem of being decreased in the distance between conductors to resultin deterioration in dielectric breakdown strength property of thecapacitor.

For example, Japanese Patent Laid-Open No. 6-163310 describes a grainboundary insulation-type semiconductor capacitor including (Ca,Sr)TiO₃as a main component, in which the composition of the semiconductorcapacitor can be controlled to result in enhancements in apparentdielectric constant and dielectric breakdown strength. There, however,is not any sample having a dielectric breakdown strength of more than1000 V/mm, while the sample has a high apparent dielectric constant of100000 or more, and thus dielectric breakdown strength property isinsufficient.

As described above, electrostatic capacitance property and dielectricbreakdown strength property are incompatible with each other, and acapacitor with a conductor/insulator composite material has the problemof having difficulty in satisfying both such properties.

The present invention has been made in view of such circumstances, andan object thereof is to allow for enhancements in apparent dielectricconstant and dielectric breakdown strength properties of a dielectrichaving a conductor/insulator composite structure.

SUMMARY OF THE INVENTION

The present invention provides the following in order to achieve theabove object.

[1] A composite structure comprising a conductor region that isconfigured from a first oxide and an insulator region that is configuredfrom a second oxide and that surrounds the conductor region, whereinhetero structure of the first oxide and the second oxide is formed.

[2] The composite structure according to [1], wherein the first oxideand the second oxide have a perovskite structure.

[3] The composite structure according to [1], wherein the first oxide isone or more oxides selected from an oxide comprising La and Ni and anoxide comprising Sr and Ru, and the second oxide is an oxide comprisingTi and one or more elements selected from Ba and Sr.

[4] The composite structure according to [2], wherein the first oxide isLaNiO₃ and/or SrRuO₃, and the second oxide is one or more selected from(Ba,Sr)TiO₃, (Bi_(0.5)Na_(0.5))TiO₃ and (Bi_(0.5)K_(0.5))TiO₃.

[5] A fired body comprising the composite structure according to any of[1] to [4].

[6] A powder comprising a particle having the composite structureaccording to any of [1] to [4].

[7] A dielectric element comprising a dielectric having the compositestructure according to any of [1] to [4].

According to the present invention, a dielectric having aconductor/insulator composite structure can be enhanced in apparentdielectric constant and dielectric breakdown strength properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a monolayer capacitor as oneexample of a dielectric element according to the present embodiment;

FIG. 2 illustrates a schematic cross-sectional view of a compositestructure according to the present embodiment;

FIG. 3 illustrates a cross-sectional view of a multilayer capacitor as amodified example of the dielectric element according to the presentembodiment;

FIG. 4 illustrates an explanatory view of a method of evaluating thepresence of hetero structure in Examples of the present invention;

FIG. 5A illustrates a TEM image of a sample according to Example 44 ofthe present invention;

FIG. 5B illustrates mapping images of the sample according to Example 44of the present invention; and

FIG. 6 illustrates a TEM image of a sample according to ComparativeExample 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail in thefollowing order based on a specific embodiment.

1. Dielectric element

1.1. Entire configuration of monolayer capacitor

1.2. Dielectric

-   -   1.2.1. Composite structure        2. Method for producing dielectric element

2.1. Powder including particle having composite structure

2.2. Fired body having composite structure

3. Effects in the present embodiment4. Modified example

1. Dielectric Element

First, a monolayer capacitor will be described as one example of adielectric element according to the present embodiment.

(1.1. Entire Configuration of Monolayer Capacitor)

As illustrated in FIG. 1, a monolayer capacitor 100 according to thepresent embodiment includes a plate-like dielectric 11, and a pair ofelectrodes 10A and 10B formed on a pair of opposite surfaces thatcorrespond to both main surfaces of the dielectric 11. The dielectric 11and the pair of electrodes 10A and 10B form a capacitor part, and thepair of electrodes 10A and 10B can be connected to an external circuitto be applied voltage, thereby allowing the dielectric 11 to exhibit apredetermined electrostatic capacitance and thus exert the function as acapacitor.

The conductive material contained in the electrodes 10A and 10B is notparticularly limited and can be arbitrarily set depending on desiredproperties, the intended use and the like. In the present embodiment,examples include silver (Ag), gold (Au), copper (Cu), platinum (Pt) andnickel (Ni).

While the dielectric 11 has a cylindrical shape in FIG. 1, the shape ofthe dielectric 11 is not particularly limited and can be arbitrarily setdepending on desired properties, the intended use and the like. Thedimension of the dielectric 11 is also not particularly limited and canbe arbitrarily set depending on desired properties, the intended use andthe like.

(1.2. Dielectric)

In the present embodiment, the dielectric 11 has a conductor/insulatorcomposite structure. Such a composite structure has a large number ofconductors connected via insulators and thus an equivalent circuit isformed where insulators, namely, dielectrics are connected serially andin parallel. An insulator exhibiting dielectric properties is thin andthe area of a conductor serving as an electrode in contact with theinsulator is large, thereby resulting in a very high apparent dielectricconstant calculated from the electrostatic capacitance. Hereinafter, acomposite structure according to the present embodiment will bedescribed in detail.

(1.2.1. Composite Structure)

A composite structure 50 is a structure including a conductor region 20and an insulator region 30 surrounding the conductor region 20, asillustrated in FIG. 2. One conductor region 20 is constituted from oneconductor particle and multiple conductor particles are bound via agrain boundary area constituting the insulator region 30 in thecomposite structure in FIG. 2. That is, a relationship between theconductor region 20 and the insulator region 30 in FIG. 2 corresponds toa relationship between a semiconductor particle and a grain boundaryphase in a grain boundary insulation-type semiconductor capacitor.

The conductor region 20 is a crystalline region that is constituted froma first oxide and that has an electrical resistivity of 1×10⁻² Ω·m orless. The conductor region 20 is preferably a region having anelectrical resistivity of 1×10⁻⁴ Ω·m or less. The insulator region 30 isa crystalline region that is constituted from a second oxide and thathas an electrical resistivity of 1×10⁴ Ω·m or more. The insulator region30 preferably has an electrical resistivity of 1×10⁶ Ω·m or more, morepreferably 1×10⁸ Ω·m or more. That is, both the conductor region 20 andthe insulator region 30 contain an oxide as a main component in thepresent embodiment.

In the present embodiment, the first oxide constituting the conductorregion 20 and the second oxide constituting the insulator region 30generate hetero structure. The “hetero structure” means that the firstoxide and the second oxide different in composition from each other arebonded on any crystal surface without any changes in respective crystalstructures. In other words, the respective crystal structures are boundwith lattice match.

Such hetero structure occurs at interface 40 between the conductorregion 20 and the insulator region 30 illustrated in FIG. 2. One surfaceof the interface 40 corresponds to an end of the crystal structure ofthe first oxide and other surface of the interface 40 corresponds to anend of the crystal structure of the second oxide. The end of the firstoxide and the end of the second oxide are continuously bound around theinterface 40. Both the crystal structures are here mutually slightlystrained in order that the first oxide and the second oxide different incrystal lattice spacing are bound with maintaining crystal latticematch. Accordingly, a hetero structure portion can be said to be astructure gradient region with a continuous change from one (forexample, first oxide) crystal structure to other (for example, secondoxide) crystal structure.

It is considered that such a structure gradient region has an effect ondielectric properties exhibited by the insulator region 30 to result inan enhancement in apparent dielectric constant of a dielectric havingthe composite structure. It is further considered that hetero structurebetween the conductor region 20 and the insulator region 30 decreasesdefects present in the insulator region 30. As a result, any conduction(short-circuiting) between adjacent conductor regions, caused throughsuch defects, can be suppressed. Accordingly, dielectric breakdownstrength property of the dielectric having the composite structure canbe enhanced regardless of a small thickness of the insulator region 30.

In the present embodiment, the insulator region 30 preferably has athickness of 1/10 or less of the diameter of the conductor region 20.From a viewpoint of sufficiently obtaining the effect of heterostructure, when a thickness of the insulator region 30 is too large, thestructure gradient region formed by hetero structure become small, notresulting in the above effect. The diameter of the conductor region 20is here defined as the average value of the longest size (major axis)and the shortest size (minor axis) of the conductor region 20.

The insulator region 30 desirably has a thickness of 1 nm or more. Whena thickness of the insulator region 30 is too small, a periphery portionof the conductor region 20 which is not covered with the insulatorregion 30 tends to be easily generated. As a result, insulationproperties tend to deteriorate and to degrade dielectric breakdownstrength property of the dielectric having the composite structure.

In the present embodiment, both the first oxide and the second oxidepreferably have a perovskite structure. When the oxide constituting theconductor region and the oxide constituting the insulator region canhave the same crystal structure, hetero structure of the first oxide andthe second oxide at the interface between the conductor region and theinsulator region easily generates, thereby allowing the structuregradient region to be sufficiently formed, to result in enhancements indielectric breakdown strength property.

The first oxide having a perovskite structure is preferably any one ofor both LaNiO₃ and SrRuO₃.

The second oxide having a perovskite structure is preferably one or moreselected from (Ba,Sr)TiO₃, (Bi_(0.5)Na_(0.5))TiO₃ and(Bi_(0.5)K_(0.5))TiO₃.

Here, (Ba,Sr)TiO₃ indicates that any one of or both Ba and Srcorrespond(s) to element(s) occupying the A site of a perovskitestructure and Ba and Sr occupy the A site in any proportion.Accordingly, in the case where (Ba,Sr)TiO₃ represents(Ba_(x)Sr_(1-x))TiO₃, x satisfies 0≤x≤1.

A case is also preferable where both the first oxide and the secondoxide have no perovskite structure. In such a case, the first oxide ispreferably one or more oxides selected from an oxide including La and Niand an oxide including Sr and Ru. Moreover, the second oxide ispreferably an oxide including Ti and one or more elements selected fromBa and Sr. A composite structure constituted by such a combinationenables the apparent dielectric constant of the dielectric to beenhanced.

The conductor region 20 may also include trace amounts of impurities,accessory component(s), and the like other than the first oxide as amain component as long as the effect of the present invention isobtained. In the present embodiment, the main component is preferablycontained in an amount of 80 mol % or more and 100 mol % or less in theentire conductor region 20. Examples of any component(s) other than themain component, namely, any component(s) not constituting any oxidehaving hetero structure, include Ca and Si.

The insulator region 30 may also include trace amounts of impurities,accessory component(s), and the like other than the second oxide as amain component as long as the effect of the present invention isobtained. In the present embodiment, the main component is preferablycontained in an amount of 80 mol % or more and 100 mol % or less in theentire insulator region 30. Examples of any component(s) other than themain component, namely, any component not constituting any oxide havinghetero structure, include Ca and Si.

The method for confirming hetero structure between the first oxide andthe second oxide in the above composite structure is not particularlylimited as long as such a method can evaluate lattice match of both therespective crystal structures at the interface between the first oxideand the second oxide.

In the present embodiment, the dielectric included in the monolayercapacitor is subjected to microsampling with a focused ion beam (FIB) toproduce a thin sample having the composite structure, and the sample isevaluated with a transmission electron microscope (TEM). Specifically,the thin sample is observed with TEM to provide a TEM image. Theobtained TEM image can be used to confirm the form of a particleconstituting the composite structure. The conductor region and theinsulator region can also be identified by STEM-EDS analysis with anenergy dispersive X-ray spectrometry (EDS) apparatus attached to ascanning transmission electron microscope (STEM). Furthermore, ahigh-resolution TEM image can be used to evaluate lattice match of boththe respective crystal structures at the interface between the firstoxide and the second oxide, and it can be thus confirmed whether or notthe first oxide and the second oxide generate hetero structure.

2. Method for Producing Dielectric Element

Next, one example of the method for producing the monolayer capacitor100 illustrated in FIG. 1 will be described below as one example of amethod for producing a dielectric element.

In the present embodiment, first, a powder including a particle havingthe composite structure with hetero structure formed is produced, thepowder is formed into a green compact, and the green compact is fired tothereby obtain a fired body. The obtained fired body has a predeterminedshape where such particles having the composite structure with heterostructure formed are mutually connected. The fired body can be subjectedto formation of electrodes thereon, thereby producing a monolayercapacitor. Hereinafter, the production method will be described indetail.

(2.1. Method for Producing Powder Including Particle Having CompositeStructure)

First, prepared is a powder including a conductor particle for formationof a conductor region. Such a powder that can be used is a powder of thefirst oxide.

Next, the conductor particle is covered with an insulator to form heterostructure. The method for covering with the insulator is notparticularly limited as long as such a method can form hetero structure.Examples include a sol gel method, an oxalate method and a hydrothermalsynthesis method. The raw material of the insulator for covering may bethe second oxide or a compound to be converted into the second oxideafter covering. Examples of the compound to be converted into the secondoxide after covering include carbonate, nitrate, hydroxide and oxide.

The present embodiment describes a method for covering the conductorparticle with the insulator by use of a hydrothermal synthesis method.Such a hydrothermal synthesis method includes dispersing a powderincluding the conductor particle, in a solvent to which the second oxideor the compound to be converted into the second oxide after covering isadded, and performing a synthesis treatment under a high temperature anda high pressure. Thus, a powder can be obtained which includes aparticle having a composite structure where the conductor particle iscovered with the insulator. Here, the amount of the raw material of theinsulator in the solvent, the synthesis temperature, the synthesis time,and the like can be controlled to thereby provide a powder including aparticle having a composite structure where the insulator forms heterostructure with the conductor particle and is grown. Accordingly, oneconductor region is present in one particle in the present embodiment.

(2.2. Method for Producing Fired Body Having Composite Structure)

Subsequently, the obtained powder is mixed by use of a ball mill or thelike. The mixing method may be conducted by wet mixing or dry mixing. Inthe case of wet mixing, a slurry after mixing is dried. The dispersionmedium during the mixing is not particularly limited, and for example,water can be used.

The method for molding the powder mixed is not particularly limited andmay be appropriately selected depending on the desired shape anddimension, and the like. In the case of press molding, a predeterminedbinder and, if necessary, an additive is added to the powder mixed andthe resultant is molded to a predetermined shape to obtain a greencompact. Alternatively, a predetermined binder and the like may be addedto the powder mixed and the resultant may be granulated to therebyobtain a granulated powder, and the granulated powder may be used toobtain a green compact.

The obtained green compact is, if necessary, subjected to a binderremoval treatment and is then fired to thereby obtain the fired bodyhaving the above composite structure. The firing conditions here are notparticularly limited as long as hetero structure is kept after thefiring, and the holding temperature is preferably 800 to 1100° C. andthe firing atmosphere is preferably in the air. The obtained fired bodyhere may be a dense fired body (sintered body) with few interparticlevoids or may be a fired body with relatively many interparticle voids.

The obtained fired body is, if necessary, polished and both mainsurfaces thereof are coated with an electrode paste and burned to forman electrode. The method for forming such an electrode is notparticularly limited and such an electrode may be formed by vapordeposition, sputtering, or the like.

The above process can be accomplished to thereby provide the monolayercapacitor illustrated in FIG. 1.

3. Effects in the Present Embodiment

In the present embodiment, the conductor (first oxide) and the insulator(second oxide) generate hetero structure at the interface therebetweenin the conductor/insulator composite structure. It is considered thathetero structure between the first oxide and the second oxide leads tothereby form a region where respective crystal structures are mutuallystrained at the interface area between the first oxide and the secondoxide. Such a region has a preferable effect on dielectric propertiesexhibited by the insulator, resulting in an enhancement in the apparentdielectric constant of the dielectric.

Furthermore, as compared with a case where the first oxide and thesecond oxide do not generate hetero structure, a crystal system ismaintained at the interface area between the first oxide and the secondoxide, although crystals are strained, and thus defects are hardlycaused in the insulator. It is considered that adjacent conductors canbe consequently inhibited from being conducted to result in enhancementsin dielectric breakdown strength property of the dielectric.

Such effects are further enhanced by a proper combination of the firstoxide and the second oxide. For example, the first oxide and the secondoxide preferably have the same crystal structure and, in particular,have a perovskite structure to result in further enhancements in theeffects. In addition, a combination with the above-mentioned oxide amongoxides having a perovskite structure allows for sufficient formation ofthe region where the respective crystal structures are mutuallystrained, resulting in further enhancements in the effects.

The effects are not obtained in a conventional grain boundaryinsulation-type semiconductor capacitor. The reason for this is becausea semiconductor particle and a grain boundary phase do not generatehetero structure in a conventional grain boundary insulation-typesemiconductor capacitor, as described below.

A representative method for producing a conventional grain boundaryinsulation-type semiconductor capacitor is as follows. For example,ceramic particles of SrTiO₃ or the like are sintered at a hightemperature of 1100° C. or more and thereafter heated at a lowertemperature than such a sintering temperature in a reducing atmosphereto thereby result in the conversion of the ceramic particles into asemiconductor. The surface of the resulting sintered body is then coatedwith a compound different in type from the ceramic particles, such asBi₂O₃, for allowing a grain boundary phase to be increased inresistivity, and the resultant is heated at a lower temperature than thetemperature at which the ceramic particles are converted into asemiconductor, thereby allowing the compound to be diffused from thesurface of the sintered body toward the grain boundary phase.

In the case of production of a grain boundary insulation-typesemiconductor capacitor according to the above production method, thegrain boundary phase formed by converting the ceramic particles into asemiconductor is considered to be amorphous because the grain boundaryphase is formed by liquid phase sintering. That is, no hetero structureis formed. There has been reported a ceramic particle in which adifferent element for an increase in resistivity is diffused in theorder of several tens nanometers and a grain boundary phase high inresistivity is formed. The amount of such a different element diffused,however, is not much more than several percentages in a high-resistivityphase formed by the diffusion. Accordingly, the change in latticeconstant of a crystal structure where such a different element isdiffused is very small with respect to the lattice constant of a crystalstructure where such a different element is not diffused. As a result,no hetero structure is formed.

4. Modified Example

While the above embodiment describes the monolayer capacitor where thedielectric is made of a monolayer, as a dielectric element, a multilayercapacitor may be exemplified which has a configuration where dielectricsare stacked.

For example, a multilayer capacitor 200 illustrated in FIG. 3 isexemplified as such a multilayer capacitor. The multilayer capacitor 200has a stacked body 24 where multiple dielectric layers 21 configuredfrom the dielectric having the composite structure and inner electrodelayers 22 are alternately stacked. A pair of terminal electrodes 23A and23B each connected to inner electrode layers 22A and 22B alternatelydisposed in the stacked body 24 is formed at both terminals of thestacked body 24. The shape of the stacked body 24 is not particularlylimited and is usually a rectangular parallelepiped shape. The dimensionthereof is also not particularly limited and may be any proper dimensiondepending on the intended use.

The thickness of one dielectric layer 21 (interlayer thickness) is notparticularly limited and can be arbitrarily set depending on desiredproperties, the intended use and the like. The interlayer thickness isusually preferably about 1 μm to 100 μm. The number of dielectric layersto be stacked is not particularly limited and can be arbitrarily setdepending on desired properties, the intended use and the like.

A known method may be used as the method for producing the multilayercapacitor 200 illustrated in FIG. 3 and the stacked body 24 is producedby, for example, producing a green chip to be the stacked body 24illustrated in FIG. 3, firing the green chip to obtain the stacked body24, thereafter printing or transferring terminal electrodes on or to thestacked body 24 and baking the resultant. Examples of the method forproducing the green chip can include usual printing method and sheetmethod by use of a paste. Such printing method and sheet method includemixing a powder including a particle having the composite structure witha vehicle where a binder is dissolved in a solvent, to provide a paste,and using the paste to form the green chip.

While embodiments of the present invention are described above, thepresent invention is not limited to the above embodiments at all and maybe modified to various aspects without departing from the scope of thepresent invention.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to Examples and Comparative Examples, but the presentinvention is not intended to be limited to the following Examples.

First, a powder including a particle having a composite structure wasproduced as follows. Each powder having a composition and a particlesize shown in Tables 1 to 3 was prepared as a powder (first oxidepowder) including a first oxide particle (conductor particle) forconstituting a conductor region.

Prepared were respective powders of TiO₂ (anatase), Ba(OH)₂.8H₂O,Al(NO₃)₃, Nb(OC₂H₅)₅, Sr(OH)₂.8H₂O, Nb₂O₅, Bi(NO₃)₃.5H₂O, KOH, and NaOHas raw materials of a second oxide (insulator) for constituting aninsulator region.

Comparative Example 1

Mixed were 1 mmol of a LaNiO₃ powder as the first oxide powder and 1mmol of a TiO₂ (anatase) powder as a raw material of the second oxide,thereby obtaining a mixed powder of the first oxide powder and the TiO₂powder. The mixed powder was added to an aqueous Ba(OH)₂.8H₂O solutionas a raw material of the second oxide, which had a concentration of Baof 0.12 M and which was prepared so that the Ba/Ti ratio with respect toTi contained in the mixed powder was 1.0, and the resultant wassubjected to an ultrasonic treatment. Thereafter, a hydrothermalsynthesis treatment at 180° C. for 3 hours was performed, therebyobtaining a powder including a particle having a composite structurewhere a conductor region (LaNiO₃) was surrounded by an insulator region(BaTiO₃).

Example 1

Weighed was 1 mmol of a RuO₂ powder as the first oxide powder, and addedto an aqueous Al(NO₃)₃ solution as a raw material of the second oxide,which was prepared so that the concentration of Al was 0.08 M, and theresultant was subjected to an ultrasonic treatment. Thereafter, ahydrothermal synthesis treatment at 220° C. for 4 hours was performed,thereby obtaining a powder including a particle having a compositestructure where a conductor region (RuO₂) was surrounded by an insulatorregion (Al₂O₃).

Example 2

Weighed was 1 mmol of a RuO₂ powder as the first oxide powder, and addedto an ethanol solution of Nb(OC₂H₅)₅ as a raw material of the secondoxide, which was prepared so that the concentration of Nb was 0.08 M, toprovide a mixture, and thereafter the mixture was dried by degassing invacuum. The mixture dried was added to water to perform a hydrothermalsynthesis treatment at 230° C. for 36 hours, thereby obtaining a powderincluding a particle having a composite structure where a conductorregion (RuO₂) was surrounded by an insulator region (Nb₂O₅).

Example 3

Mixed were 1 mmol of a RuO₂ powder as the first oxide powder and 1 mmolof a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Sr(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Sr of 0.06 M and whichwas prepared so that the Sr/Ti ratio with respect to Ti contained in themixed powder was 3.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (RuO₂) was surrounded by an insulator region (SrTiO₃).

Example 4

Mixed were 1 mmol of a RuO₂ powder as the first oxide powder and 1 mmolof a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.06 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 3.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (RuO₂) was surrounded by an insulator region (BaTiO₃).

Examples 5 to 8

The same method as in each of Examples 1 to 4 was performed except thatthe first oxide powder in each of Examples 1 to 4 was changed to an IrO₂powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (IrO₂) was surrounded by aninsulator region.

Examples 9 to 12

The same method as in each of Examples 1 to 4 was performed except thatthe first oxide powder in each of Examples 1 to 4 was changed to a SnO₂powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (SnO₂) was surrounded by aninsulator region.

Examples 13 and 14

The same method as in each of Examples 1 and 2 was performed except thatthe first oxide powder in each of Examples 1 and 2 was changed to aLaMnO₃ powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaMnO₃) was surrounded byan insulator region.

Examples 15 and 16

The same method as in each of Examples 1 and 2 was performed except thatthe first oxide powder in each of Examples 1 and 2 was changed to aLaCoO₃ powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaCoO₃) was surrounded byan insulator region.

Examples 17 and 18

The same method as in each of Examples 1 and 2 was performed except thatthe first oxide powder in each of Examples 1 and 2 was changed to aLaNiO₃ powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaNiO₃) was surrounded byan insulator region.

Examples 19 and 20

The same method as in each of Examples 1 and 2 was performed except thatthe first oxide powder in each of Examples 1 and 2 was changed to aSrRuO₃ powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (SrRuO₃) was surrounded byan insulator region.

Example 21

Mixed were 1 mmol of a LaMnO₃ powder as the first oxide powder and 0.2mmol of a Nb₂O₅ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and Nb₂O₅. The mixedpowder was added to an aqueous KOH solution as a raw material of thesecond oxide, which had a concentration of K of 1.0 M and which wasprepared so that the K/Nb ratio with respect to Nb contained in themixed powder was 10 at a molar ratio, and a hydrothermal synthesistreatment at 230° C. for 10 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (LaMnO₃) was surrounded by an insulator region (KNbO₃).

Examples 22 and 23

The same method as in each of Examples 3 and 4 was performed except thatthe first oxide powder in each of Examples 3 and 4 was changed to aLaMnO₃ powder, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaMnO₃) was surrounded byan insulator region.

Example 24

Mixed were 1 mmol of a LaMnO₃ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. Next,Bi(NO₃)₃.5H₂O as a raw material of the second oxide was weighed so thatthe Bi/Ti ratio was 0.5 at a molar ratio, 50 mL of pure water was addedthereto and the resultant was subjected to an ultrasonic treatment,thereby obtaining a solution. Thereafter, KOH as a raw material of thesecond oxide was added for preparation so that the concentration of thesolution was 14.4 M, and the resultant was again subjected to anultrasonic treatment. The resulting mixed powder was added to the abovesolution, and a hydrothermal synthesis treatment at 160° C. for 6 hourswas performed, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaMnO₃) was surrounded byan insulator region ((Bi_(0.5)K_(0.5))TiO₃).

Example 25

Mixed were 1 mmol of a LaMnO₃ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. Next,Bi(NO₃)₃.5H₂O as a raw material of the second oxide was weighed so thatthe Bi/Ti ratio was 0.5 at a molar ratio, 50 mL of pure water was addedthereto and the resultant was subjected to an ultrasonic treatment,thereby obtaining a solution. Thereafter, NaOH as a raw material of thesecond oxide was added for preparation so that the concentration of thesolution was 14.4 M, and the resultant was again subjected to anultrasonic treatment. The resulting mixed powder was added to the abovesolution, and a hydrothermal synthesis treatment at 160° C. for 6 hourswas performed, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaMnO₃) was surrounded byan insulator region ((Bi_(0.5)Na_(0.5))TiO₃).

Examples 26 to 30

The same method as in each of Examples 21 to 25 was performed exceptthat the first oxide powder in each of Examples 21 to 25 was changed toa LaCoO₃ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (LaCoO₃) was surroundedby an insulator region.

Example 31

The same method as in Example 21 was performed except that the firstoxide powder in Example 21 was changed to a LaNiO₃ powder, therebyobtaining a powder including a particle having a composite structurewhere a conductor region (LaNiO₃) was surrounded by an insulator region.

Example 32

The same method as in Example 21 was performed except that the firstoxide powder in Example 21 was changed to a SrRuO₃ powder, therebyobtaining a powder including a particle having a composite structurewhere a conductor region (SrRuO₃) was surrounded by an insulator region.

Example 33

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Sr(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Sr of 0.12 M and whichwas prepared so that the Sr/Ti ratio with respect to Ti contained in themixed powder was 6.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (La₂NiO₄) was surrounded by an insulator region(Sr₂TiO₄).

Example 34

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Sr(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Sr of 0.03 M and whichwas prepared so that the Sr/Ti ratio with respect to Ti contained in themixed powder was 1.5 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (La₂NiO₄) was surrounded by an insulator region(SrTi₂O₅).

Example 35

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.12 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 6.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (La₂NiO₄) was surrounded by an insulator region(Ba₂TiO₄).

Example 36

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.03 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 1.5 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 3 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (La₂NiO₄) was surrounded by an insulator region(BaTi₂O₅).

Example 37

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O+Sr(OH)₂.8H₂O solution as araw material of the second oxide, which had a concentration of Ba of0.03 M and a concentration of Sr of 0.03 M, and which was prepared sothat the Ba/Sr ratio was 1.0 at a molar ratio and the (Ba+Sr)/Ti ratiowith respect to Ti contained in the mixed powder was 3.0 at a molarratio, and the resultant was subjected to an ultrasonic treatment.Thereafter, a hydrothermal synthesis treatment at 200° C. for 3 hourswas performed, thereby obtaining a powder including a particle having acomposite structure where a conductor region (La₂NiO₄) was surrounded byan insulator region ((Ba_(0.5)Sr_(0.5))TiO₃).

Examples 38 to 42

The same method as in each of Examples 33 to 37 was performed exceptthat the first oxide powder in each of Examples 33 to 37 was changed toa SrRu₂O₅ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (SrRu₂O₅) was surroundedby an insulator region.

Examples 43 and 44

The same method as in each of Examples 22 and 23 was performed exceptthat the first oxide powder in each of Examples 22 and 23 was changed toa LaNiO₃ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (LaNiO₃) was surroundedby an insulator region.

Example 45

Mixed were 1 mmol of a LaNiO₃ powder as the first oxide powder and 0.1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O+Sr(OH)₂.8H₂O solution as araw material of the second oxide, which had a concentration of Ba of0.03 M and a concentration of Sr of 0.03 M, and which was prepared sothat the Ba/Sr ratio was 1.0 at a molar ratio and the (Ba+Sr)/Ti ratiowith respect to Ti contained in the mixed powder was 3.0 at a molarratio, and the resultant was subjected to an ultrasonic treatment.Thereafter, a hydrothermal synthesis treatment at 200° C. for 3 hourswas performed, thereby obtaining a powder including a particle having acomposite structure where a conductor region (LaNiO₃) was surrounded byan insulator region ((Ba_(0.5)Sr_(0.5))TiO₃).

Examples 46 and 47

The same method as in each of Examples 24 and 25 was performed exceptthat the first oxide powder in each of Examples 24 and 25 was changed toa LaNiO₃ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (LaNiO₃) was surroundedby an insulator region.

Examples 48 and 49

The same method as in each of Examples 22 and 23 was performed exceptthat the first oxide powder in each of Examples 22 and 23 was changed toa SrRuO₃ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (SrRuO₃) was surroundedby an insulator region.

Example 50

The same method as in Example 45 was performed except that the firstoxide powder in Example 45 was changed to a SrRuO₃ powder, therebyobtaining a powder including a particle having a composite structurewhere a conductor region (SrRuO₃) was surrounded by an insulator region.

Examples 51 and 52

The same method as in each of Examples 24 and 25 was performed exceptthat the first oxide powder in each of Examples 24 and 25 was changed toa SrRuO₃ powder, thereby obtaining a powder including a particle havinga composite structure where a conductor region (SrRuO₃) was surroundedby an insulator region.

Example 53

Weighed was 1 mmol of a RuO₂ powder as the first oxide powder, and addedto an aqueous Al(NO₃)₃ solution as a raw material of the second oxide,which was prepared so that the concentration of Al was 0.08 M, and theresultant was subjected to an ultrasonic treatment. Thereafter, ahydrothermal synthesis treatment at 220° C. for 1.6 hours was performed,thereby obtaining a powder including a particle having a compositestructure where a conductor region (RuO₂) was surrounded by an insulatorregion (Al₂O₃).

Example 54

Mixed were 1 mmol of a LaMnO₃ powder as the first oxide powder and 1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.06 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 3.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 1.2 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (LaMnO₃) was surrounded by an insulator region(BaTiO₃).

Example 55

Mixed were 1 mmol of a La₂NiO₄ powder as the first oxide powder and 1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.03 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 1.5 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 1.2 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (La₂NiO₄) was surrounded by an insulator region(BaTi₂O₅).

Example 56

Mixed were 1 mmol of a LaNiO₃ powder as the first oxide powder and 1mmol of a TiO₂ powder as a raw material of the second oxide, therebyobtaining a mixed powder of the first oxide powder and TiO₂. The mixedpowder was added to an aqueous Ba(OH)₂.8H₂O solution as a raw materialof the second oxide, which had a concentration of Ba of 0.06 M and whichwas prepared so that the Ba/Ti ratio with respect to Ti contained in themixed powder was 3.0 at a molar ratio, and the resultant was subjectedto an ultrasonic treatment. Thereafter, a hydrothermal synthesistreatment at 200° C. for 1.2 hours was performed, thereby obtaining apowder including a particle having a composite structure where aconductor region (LaNiO₃) was surrounded by an insulator region(BaTiO₃).

It was evaluated whether or not the first oxide and the second oxideformed hetero structure with each other in the composite structure ofthe particle contained in each of the resulting powders. First,microsampling of the particle was performed according to FIB, andthinning was made, thereby producing a TEM sample. The resulting TEMsample was observed with TEM (JEM-2100F manufactured by JEOL Ltd.),thereby identifying the first oxide particle constituting the conductorregion and the grain boundary phase constituting the insulator region inthe composite structure.

Ten of such particles having the composite structure were selected inthe TEM image acquired, and four measurement points MPs different inlocation by 90° around the interface between the conductor region andthe insulator region in each of such particles, as illustrated in FIG.4, were observed with high-resolution TEM, thereby evaluating whether ornot the first oxide and the second oxide formed hetero structure witheach other. A case where the number of particles with hetero structureobserved at three or more of such four points was seven or more amongten of such particles was evaluated to be a case where the first oxideand the second oxide formed hetero structure with each other in thecomposite structure. The results are shown in Tables 1 to 3.

FIG. 5A illustrates a TEM image representing hetero structure of thefirst oxide with the second oxide in the powder of Example 44, and FIG.6 illustrates a TEM image representing no hetero structure of the firstoxide with the second oxide in the powder of Comparative Example 1.

The conductor region and the insulator region were subjected toconstituent element mapping according to STEM-EDS analysis. FIG. 5Billustrates mapping images with respect to Example 44. The left in FIG.5B illustrates a mapping image of a Ti element, and the right in FIG. 5Billustrates a mapping image of a Ni element. While not illustrated, amapping image of a Ba element was similar to that of a Ti element, and amapping image of a La element was similar to of a Ni element.

It was further confirmed from the TEM image that the diameter of theconductor region was in the range from 500 to 600 nm and the thicknessof the insulator region was in the range from 30 to 50 nm in each sampleaccording to Comparative Example 1 and Examples 1 to 52. It was alsoconfirmed that the diameter of the conductor region was in the rangefrom 200 to 220 nm and the thickness of the insulator region was in therange from 15 to 20 nm in each sample according to Examples 53 to 56.

Each sample according to Comparative Example 1 and Examples 1 to 56 wassubjected to measurement and analysis with an XRD measurement apparatus(Smartlab manufactured by Rigaku Corporation) according to an X-raydiffraction method, and it was confirmed that oxide crystalsconstituting the conductor region and the insulator region contained ineach sample according to Comparative Example 1 and Examples 1 to 56corresponded to substances shown in Table 1.

Examples 1 to 56 and Comparative Example 1

Next, 2% by weight of polyvinyl butyral was added to each of the powdersobtained, and subjected to powder compacting, thereby producing eachdisc-like formed body having a diameter of about 10 mm and a thicknessof about 1 mm. The resulting formed body was subjected to removal of thebinder at 600° C., and thereafter fired at 1000° C. for 2 hours, therebyobtaining a fired body (dielectric) having a composite structure. Au wassputtered on both main surfaces of the resulting fired body to therebyform an electrode, thereby producing each capacitor of Examples 1 to 56and Comparative Example 1.

It was evaluated whether or not the first oxide and the second oxideformed hetero structure with each other in the composite structure ofthe dielectric constituting each of the resulting capacitors. First,microsampling of the dielectric of each of the capacitors was performedaccording to FIB, and thinning was made, thereby producing a TEM sample.The resulting TEM sample was observed with TEM (JEM-2100F manufacturedby JEOL Ltd.), thereby identifying the first oxide particle constitutingthe conductor region and the grain boundary phase constituting theinsulator region in the composite structure.

Ten of such first oxide particles were selected in the TEM imageacquired, and four measurement points MPs different in location by 90°around the interface 40 between the conductor particle (conductor region20) and the grain boundary phase (insulator region 30) in each of suchparticles, as illustrated in FIG. 4, were observed with high-resolutionTEM, thereby evaluating whether or not the first oxide and the secondoxide formed hetero structure with each other. A case where the numberof particles with hetero structure observed at three or more of suchfour points was seven or more among ten of such particles was evaluatedto be a case where the first oxide and the second oxide formed heterostructure with each other in the composite structure. The results areshown in Tables 1 to 3.

Next, the capacitor was subjected to measurement of the dielectricconstant and the dielectric breakdown strength thereof. The dielectricconstant (no unit) was calculated from the distance between electrodes,the area of each electrode, and electrostatic capacitance which weremeasured with a digital LCR meter (4284A manufactured by HP DevelopmentCompany, L.P.) in conditions of room temperature of 25° C., a frequencyof 1 kHz and a level of signal input (measurement voltage) of 1.0 Vrms.A higher dielectric constant is more preferable. In the presentExamples, a sample having a dielectric constant of 12000 or more wasdefined as “Good”, a sample having a dielectric constant of 15000 ormore was defined as “Particularly Good” and a sample having a dielectricconstant of 18000 or more was defined as “Further Good”. The results areshown in Tables 1 to 3.

The dielectric breakdown strength is determined by gradually increasingthe direct voltage applied between electrodes, dividing the voltage atthe occurrence of insulation breakdown by the thickness of the insulatorlayers and converting the resulting quotient into a value permillimeter. In the present Examples, a sample having an averagedielectric breakdown strength of 3.0 kV/mm or more was defined as “Good”and a sample having an average dielectric breakdown strength of 3.5kV/mm or more was defined as “Particularly Good”. The results are shownin Tables 1 to 3.

TABLE 1 Capacitor Powder Composite Composite structure structureProperties Conductor region Presence or Presence or Dielectric Firstoxide particle Insulator region absence of absence of Dielectricbreakdown Diameter Oxide Second oxide hetero hetero constant strength(nm) species Oxide species structure structure (—) (kV/mm) Comparative500 LaNiO₃ BaTiO₃ Absence Absence 14000 2.5 Example 1 Example 1 500 RuO₂Al₂O₃ Presence Presence 12000 3.2 Example 2 500 RuO₂ Nb₂O₅ PresencePresence 12000 3.1 Example 3 500 RuO₂ SrTiO₃ Presence Presence 14000 3.0Example 4 500 RuO₂ BaTiO₃ Presence Presence 14500 3.0 Example 5 500 IrO₂Al₂O₃ Presence Presence 12000 3.2 Example 6 500 IrO₂ Nb₂O₅ PresencePresence 12000 3.2 Example 7 500 IrO₂ SrTiO₃ Presence Presence 14000 3.0Example 8 500 IrO₂ BaTiO₃ Presence Presence 14500 3.0 Example 9 500 SnO₂Al₂O₃ Presence Presence 12000 3.2 Example 10 500 SnO₂ Nb₂O₅ PresencePresence 12000 3.2 Example 11 500 SnO₂ SrTiO₃ Presence Presence 140003.0 Example 12 500 SnO₂ BaTiO₃ Presence Presence 14500 3.0 Example 13500 LaMnO₃ Al₂O₃ Presence Presence 12000 3.2 Example 14 500 LaMnO₃ Nb₂O₅Presence Presence 12500 3.1 Example 15 500 LaCoO₃ Al₂O₃ PresencePresence 12000 3.2 Example 16 500 LaCoO₃ Nb₂O₅ Presence Presence 125003.1 Example 17 500 LaNiO₃ Al₂O₃ Presence Presence 12000 3.2 Example 18500 LaNiO₃ Nb₂O₅ Presence Presence 12500 3.1 Example 19 500 SrRuO₃ Al₂O₃Presence Presence 12000 3.2 Example 20 500 SrRuO₃ Nb₂O₅ PresencePresence 12500 3.1

TABLE 2 Capacitor Powder Composite Composite structure structureProperties Conductor region Presence or Presence or Dielectric Firstoxide particle Insulator region absence of absence of Dielectricbreakdown Diameter Oxide Second oxide hetero hetero constant strength(nm) species Oxide species structure structure (—) (kV/mm) Example 21500 LaMnO₃ KNbO₃ Presence Presence 13000 3.7 Example 22 500 LaMnO₃SrTiO₃ Presence Presence 14000 3.6 Example 23 500 LaMnO₃ BaTiO₃ PresencePresence 14500 3.5 Example 24 500 LaMnO₃ (Bi_(0.5)K_(0.5))TiO₃ PresencePresence 14000 3.5 Example 25 500 LaMnO₃ (Bi_(0.5)Na_(0.5))TiO₃ PresencePresence 14000 3.5 Example 26 500 LaCoO₃ KNbO₃ Presence Presence 130003.7 Example 27 500 LaCoO₃ SrTiO₃ Presence Presence 14000 3.6 Example 28500 LaCoO₃ BaTiO₃ Presence Presence 14500 3.5 Example 29 500 LaCoO₃(Bi_(0.5)K_(0.5))TiO₃ Presence Presence 14000 3.5 Example 30 500 LaCoO₃(Bi_(0.5)Na_(0.5))TiO₃ Presence Presence 14000 3.5 Example 31 500 LaNiO₃KNbO₃ Presence Presence 13000 3.7 Example 32 500 SrRuO₃ KNbO₃ PresencePresence 13000 3.7 Example 33 500 La₂NiO₄ Sr₂TiO₄ Presence Presence15200 3.3 Example 34 500 La₂NiO₄ SrTi₂O₅ Presence Presence 15700 3.1Example 35 500 La₂NiO₄ Ba₂TiO₄ Presence Presence 16300 3.2 Example 36500 La₂NiO₄ BaTi₂O₅ Presence Presence 17200 3.2 Example 37 500 La₂NiO₄(Ba_(0.5)Sr_(0.5))TiO₃ Presence Presence 16200 3.3 Example 38 500SrRu₂O₅ Sr₂TiO₄ Presence Presence 15300 3.1 Example 39 500 SrRu₂O₅SrTi₂O₅ Presence Presence 15600 3.2 Example 40 500 SrRu₂O₅ Ba₂TiO₄Presence Presence 16600 3.4 Example 41 500 SrRu₂O₅ BaTi₂O₅ PresencePresence 17000 3.4 Example 42 500 SrRu₂O₅ (Ba_(0.5)Sr_(0.5))TiO₃Presence Presence 16800 3.2 Example 43 500 LaNiO₃ SrTiO₃ PresencePresence 18700 3.7 Example 44 500 LaNiO₃ BaTiO₃ Presence Presence 189003.5 Example 45 500 LaNiO₃ (Ba_(0.5)Sr_(0.5))TiO₃ Presence Presence 190003.6 Example 46 500 LaNiO₃ (Bi_(0.5)K_(0.5))TiO₃ Presence Presence 183003.6 Example 47 500 LaNiO₃ (Bi_(0.5)Na_(0.5))TiO₃ Presence Presence 182003.6 Example 48 500 SrRuO₃ SrTiO₃ Presence Presence 19100 3.7 Example 49500 SrRuO₃ BaTiO₃ Presence Presence 19900 3.5 Example 50 500 SrRuO₃(Ba_(0.5)Sr_(0.5))TiO₃ Presence Presence 19500 3.7 Example 51 500 SrRuO₃(Bi_(0.5)K_(0.5))TiO₃ Presence Presence 18100 3.6 Example 52 500 SrRuO₃(Bi_(0.5)Na_(0.5))TiO₃ Presence Presence 18300 3.6

TABLE 3 Capacitor Powder Composite Composite structure structureProperties Conductor region Presence or Presence or Dielectric Firstoxide particle Insulator region absence of absence of Dielectricbreakdown Diameter Oxide Second oxide hetero hetero constant strength(nm) species Oxide species structure structure (—) (kV/mm) Example 53200 RuO₂ Al₂O₃ Presence Presence 12500 3.3 Example 54 200 LaMnO₃ BaTiO₃Presence Presence 14000 3.8 Example 55 200 La₂NiO₄ BaTi₂O₅ PresencePresence 16800 3.7 Example 56 200 LaNiO₃ BaTiO₃ Presence Presence 180003.7

As clear from Tables 1 and 2, and FIGS. 5A and 6, it could be confirmedin comparison of Comparative Example 1 with Example 44 that the firstoxide and the second oxide formed hetero structure with each other inthe powder according to Example 44. It could also be confirmed that suchhetero structure in the powder was also kept in a fired body afterfiring. As a result, enhancements in apparent dielectric constant anddielectric breakdown strength properties of the capacitor could beconfirmed. Even in the case where the first oxide constituting theconductor region and the second oxide constituting the insulator regionwere various oxides, it could be confirmed that the first oxide and thesecond oxide were in hetero structure with each other to result inenhancements in apparent dielectric constant and dielectric breakdownstrength properties.

Horizontal lattice fringes were continued between the left section(conductor region 20) and the right section (insulator region 30) of theinterface 40 in FIG. 5A, and it was thus found that hetero structure isformed between the first oxide and the second oxide. It is noted that awhite line representing the interface 40 in FIG. 5A means not theemergence of the interface 40 as a white line in the TEM image, but aline added for clearly indicating the interface 40. On the other hand,lattice fringes were not continued between and were overlapped in theleft section (conductor region 20) and the right section (insulatorregion 30) of the TEM image to cause any unclear section 60 in FIG. 6,and it was thus found that hetero structure of the first oxide and thesecond oxide was not formed.

FIG. 5A illustrates an enlarged view of a square section VA in FIG. 5B,and it can be seen that neither a Ba element nor a Ti element is presentand La and Ni elements are present in the conductor region 20, andneither a La element nor a Ni element is present and Ba and Ti elementsare present in the insulator region 30 in FIG. 5B. It could also beconfirmed from observation of only peaks attributed to LaNiO₃ and BaTiO₃in X-ray diffraction analysis that the oxide constituting the conductorregion was LaNiO₃ and the oxide constituting the insulator region wasBaTiO₃.

It could also be confirmed from Table 2 that apparent dielectricconstant and dielectric breakdown strength properties were more enhancedin the case where both the first oxide and the second oxide had aperovskite structure. In particular, it could be confirmed that apparentdielectric constant and dielectric breakdown strength properties werestill more enhanced in the case where the first oxide and the secondoxide were each a predetermined oxide.

It could be confirmed from Table 3 that the same effects were obtainedeven in the case where the conductor particle constituting the conductorregion had a different diameter.

The present invention provides a conductor/insulator composite structurethat can allow dielectric breakdown strength property to be enhancedwith apparent dielectric constant being kept. A dielectric having such acomposite structure is suitable for various electronic equipment, energystorage devices, and the like.

REFERENCE SIGNS LIST

-   -   100 . . . monolayer capacitor    -   10A, 10B . . . terminal electrode    -   11 . . . dielectric    -   20 . . . conductor region    -   30 . . . insulator region    -   40 . . . interface

What is claimed is:
 1. A composite structure comprising a conductorregion that is configured from a first oxide, and an insulator regionthat is configured from a second oxide and that surrounds the conductorregion, wherein hetero structure of the first oxide and the second oxideis formed.
 2. The composite structure according to claim 1, wherein thefirst oxide and the second oxide have a perovskite structure.
 3. Thecomposite structure according to claim 1, wherein the first oxide is oneor more oxides selected from an oxide comprising La and Ni and an oxidecomprising Sr and Ru, and the second oxide is an oxide comprising Ti andone or more elements selected from Ba and Sr.
 4. The composite structureaccording to claim 2, wherein the first oxide is LaNiO₃ and/or SrRuO₃,and the second oxide is one or more selected from (Ba,Sr)TiO₃,(Bi_(0.5)Na_(0.5))TiO₃ and (Bi_(0.5)K_(0.5))TiO₃.
 5. A fired bodycomprising the composite structure according to claim
 1. 6. A fired bodycomprising the composite structure according to claim
 2. 7. A fired bodycomprising the composite structure according to claim
 3. 8. A fired bodycomprising the composite structure according to claim
 4. 9. A powdercomprising a particle having the composite structure according toclaim
 1. 10. A dielectric element comprising a dielectric having thecomposite structure according to claim
 1. 11. A dielectric elementcomprising a dielectric having the composite structure according toclaim
 2. 12. A dielectric element comprising a dielectric having thecomposite structure according to claim
 3. 13. A dielectric elementcomprising a dielectric having the composite structure according toclaim 4.